BACKGROUND OF THE INVENTION
[0001] The present invention relates to an accumulator fuel injection apparatus.
[0002] An accumulator fuel injection apparatus, generally known as a common rail type fuel
injection apparatus, is preferably used to inject fuel into a diesel engine. According
to the accumulator fuel injection apparatus, a common accumulator piping (i.e., common
rail) is provided to supply fuel to each cylinder of the engine. A supply pump is
provided to supply pressurized fuel into this common rail so that a hydraulic pressure
of the fuel in the common rail is maintained at a predetermined level. The accumulated
fuel of the common rail is introduced into each fuel injector via a fuel supply pipe.
[0003] The accumulated fuel supplied to the fuel injector is chiefly injected into a combustion
chamber of each cylinder. However, part of the accumulated fuel is used to control
the fuel injector. This kind of control fuel is introduced into a control chamber.
An electromagnetic valve opens or closes a fuel discharge passage of the control chamber
to adjust a hydraulic pressure of the control chamber. The control chamber controls
opening and closing of a needle valve that determines injection and shutoff periods
of the fuel injector. The electromagnetic valve discharges the fuel from its valve
opening to a low-pressure return passage via a switching leak passage. Furthermore,
when the fuel leaks from any slide portion of the fuel injector, the fuel returns
via a stationary passage to the low-pressure return passage.
[0004] The electromagnetic valve has an armature driven by a solenoid to open-and-close
control the valve opening of the electromagnetic valve. The armature is accommodated
in an armature chamber. This armature chamber is filled with the fuel to stabilize
the operation of the armature. As an arrangement for introducing the fuel into the
armature chamber, the armature chamber may be located downstream of the valve opening
of the electromagnetic valve in the switching leak passage, as disclosed in the published
Japanese Patent Application No. Kokai 9-42106, corresponding to the United States
Patent Application No. 08/686,774.
[0005] However, when incorporated into recent advanced engines, the above-described fuel
injection apparatus cannot satisfy various requirements for realizing precise engine
controls. More specifically, a great amount of bubbles are generated in the vicinity
of a valve opening of the electromagnetic valve when the hydraulic pressure of the
accumulated fuel in the control chamber abruptly reduces to a lower value in response
to the valve opening operation. The generated bubbles enter the armature chamber.
When the armature chamber is filled with bubble-containing fuel, the armature does
not operate stably. Furthermore, the fuel leak amount varies depending on engine operating
conditions, causing changes in the hydraulic pressure of the armature chamber and
in the bubble amount so that the operation varies in a complicated manner. When realizing
the precise engine controls, such unstable operation of the armature (i.e., open and
close control of the electromagnetic valve) will cause various problems including
fluctuation of the fuel injection amount with respect to a set value.
[0006] According to another conventional method of introducing the fuel into the armature
chamber, it is possible to form a dead alley branching from the switching leak passage
at a portion just downstream of a valve opening of the electromagnetic valve. The
armature chamber is provided at the dead end of this alley so as to prevent bubbles
generated at the valve opening of the electromagnetic valve from directly entering
the armature chamber. However, this arrangement is disadvantageous in that air may
enter the armature chamber during installation and the residual air in the armature
chamber cannot be discharged easily. This sensitively changes environment of the armature
depending on the engine operating conditions. The armature is soaked in the fuel in
some cases and exposed to the air in other cases. This is not preferable in realizing
accurate engine control.
[0007] Furthermore, according to the above-described accumulator fuel injection apparatus,
when the needle valve is closed, a hydraulic pressure of the armature chamber changes
abruptly. Operation of the electromagnetic valve is not stabilized. Fig. 14 shows
a variation of a valve lift amount relative to elapse of time. Due to unstable operation
of the electromagnetic valve, the needle valve causes a large bounce after the needle
valve is once seated to stop the fuel supply. Such a bouncing behavior of the needle
valve causes a significant delay in the shutoff operation of the fuel injection. As
a result, an actual fuel injection amount exceeds a set value predetermined based
on engine operating conditions, such as engine load or the like. The valve bouncing
behavior is not constant and variable depending on engine operating conditions as
well as individual differences of needle valves. Accordingly, as a matter of practical
problem, correcting the error caused between the actual fuel injection amount and
the set value is difficult. The engine controls cannot be accurately performed.
SUMMARY OF THE INVENTION
[0008] In view of the problems encountered in the prior art, an object of the present invention
is to provide an accumulator fuel injection apparatus which is capable of stabilizing
the armature operation of the electromagnetic valve and realizing accurate engine
controls.
[0009] Another object of the present invention is to provide an accumulator fuel injection
apparatus which is capable of suppressing the valve bouncing behavior during a valve
closing operation, thereby realizing accurate engine controls.
[0010] In order to accomplish this and other related objects, the present invention provides
an accumulator fuel injection apparatus comprising a fuel injector, an accumulator
pipe for supplying pressurized fuel to the fuel injector, a control chamber for open-and-close
controlling a needle valve that determines injection and shutoff periods of the fuel
injector, an electromagnetic valve for adjusting a hydraulic pressure of the control
chamber, and a stabilizing means provided for stabilizing behavior of the fuel used
to control the fuel injector.
[0011] Preferably, the electromagnetic valve comprises an armature driven by a solenoid
to open-and-close control a valve opening of the electromagnetic valve. The armature
is accommodated in an armature chamber into which the fuel is introduced. And, the
stabilizing means is a passage for discharging bubbles or residual air from the armature
chamber.
[0012] Preferably, the stabilizing means is a damper element provided in a return passage
which returning part of the pressurized fuel from the fuel injector to a fuel tank
via a return pipe. The damper element is provided at a portion downstream of the electromagnetic
valve for suppressing increase in a hydraulic pressure of fuel flowing in the return
passage.
[0013] According to one aspect of the present invention, the fuel injector introduces part
of accumulated fuel into a control chamber to open-and-close control a needle valve
according to a hydraulic pressure of the introduced fuel. The needle valve determines
injection and shutoff periods of the fuel injector. An electromagnetic valve opens
and closes a fuel discharge passage of the control chamber to adjust a hydraulic pressure
in the control chamber, thereby opening or closing the needle valve. The fuel injector
comprises a switching leak passage for returning discharged fuel from a valve opening
of the electromagnetic valve to a low-pressure return passage, and a stationary leak
passage for returning fuel leaking from slide portions of the fuel injector to the
low-pressure return passage. The electromagnetic valve comprises an armature chamber
for accommodating an armature driven by a solenoid to open-and-close control the valve
opening of the electromagnetic valve. The fuel is introduced into the armature chamber.
Furthermore, the switching leak passage directly connects the valve opening of the
electromagnetic valve and the low-pressure return passage. The armature chamber is
provided in the stationary leak passage. A downstream portion of the stationary leak
passage positioned downstream of the armature chamber communicates with an upper portion
of the armature chamber.
[0014] The fuel flowing in the switching leak passage may contain a great amount of bubbles
generated at the valve opening of the electromagnetic valve. However, as the valve
opening of the electromagnetic valve directly communicates with the return passage,
the bubbles move toward the return passage without directly entering the armature
chamber.
[0015] The residual air contained in the armature chamber during installation of the apparatus
moves to the upper portion of the armature chamber when the leaking fuel starts flowing
into the stationary leak passage. As the downstream portion of the stationary leak
passage is connected to the upper portion of the armature chamber, the air exits out
of the armature chamber and moves to the downstream portion of the stationary leak
passage. The armature chamber is filled with fuel so that the armature is not exposed
to air.
[0016] The fuel leaking from each slide portion contains few bubbles. In the armature chamber,
few bubbles are generated. Accordingly, after moving to the upper portion of the armature
chamber, the bubbles quickly exit out of the armature chamber and come to the downstream
portion of the stationary leak passage in the same manner as the above-described residual
air.
[0017] Thus, the armature movement is stabilized and the electromagnetic valve operates
appropriately.
[0018] Preferably, the downstream portion of the stationary leak passage is connected to
a ceiling opening of the armature chamber which is located at the highest point of
the armature chamber. With this arrangement, the residual air and the bubbles can
smoothly exit out of the armature chamber to the downstream portion of the stationary
leak passage.
[0019] Preferably, the stationary leak passage has a check valve provided between the armature
chamber and a merging portion to the switching leak passage for limiting flow of the
fuel in a single direction directing from the armature chamber to the merging portion.
[0020] The provision of the check valve surely prevents the bubble-containing fuel from
flowing into the armature chamber from the switching leak passage. Thus, it becomes
possible to eliminate the adverse influence of the bubbles generated at the valve
opening of the electromagnetic valve.
[0021] According to another aspect of the present invention, pressurized fuel is supplied
to the fuel injector from the accumulator pipe. A return passage is provided for returning
part of the pressurized fuel from the fuel injector to a fuel tank via a return pipe.
A control chamber is provided in the return passage for open-and-close controlling
the needle valve that determines injection and shutoff periods of the fuel injector.
An electromagnetic valve is provided downstream of the control chamber for controlling
communication and isolation between the control chamber and the return pipe. And,
a damper element is provided in the return passage at a portion downstream of the
electromagnetic valve for suppressing increase in a hydraulic pressure of fuel flowing
in the return passage.
[0022] According to this arrangement, the damper element suppresses the increase in the
hydraulic pressure of the fuel flowing in the downstream portion of the electromagnetic
valve, eliminating fluctuation of fuel pressure in the fuel injector and stabilizing
operation of the electromagnetic valve. Thus, the bouncing phenomenon of the needle
valve is eliminated, and accurate engine control is realized.
[0023] Preferably, the damper element comprises a pressure-receiving plate facing the return
passage and retractable in response to the increase of hydraulic pressure of the fuel
flowing in the return passage.
[0024] When the pressure-receiving plate shifts backward, a substantial volume of the downstream
portion of the return passage increases so as to cancel the increase of the fuel pressure.
[0025] Preferably, the damper element is accommodated in a connection member connecting
the fuel injector and the return pipe. The connection member constitutes part of the
return passage.
[0026] The connection member is located just downstream of the fuel injector, and therefore
the connection member is closer to the electromagnetic valve. This arrangement allows
the damper element accommodated in the connection member to quickly increase the downstream
volume of the return passage in response to the increased fuel pressure. Thus, the
valve bouncing behavior can be effectively eliminated. The damper element can be easily
accommodated in the connection member. Thus, the present invention requires no design
modification in the overall arrangement of the apparatus.
[0027] Preferably, the connection member comprises a cylindrical housing connected to the
fuel injector at one end. The cylindrical housing has at least one through hole formed
on a cylindrical wall for communicating an inside space of the cylindrical housing
with the return pipe. The damper element comprises a pressure-receiving plate made
of a resiliently deflectable thin plate disposed normal to an axis of the cylindrical
housing to close the other end of the cylindrical housing.
[0028] By simply closing the other end of the housing with the pressure-receiving plate,
the damper element can be easily constituted. Furthermore, the increase of the fuel
pressure can be effectively canceled because the pressure-receiving plate is disposed
normal to the axial direction corresponding to the flow direction of the fuel in the
housing.
[0029] Preferably, two pairs of through holes are provided at symmetrical positions on the
cylindrical housing corresponding to radial lines crossing normal to each other. The
two pairs of through holes are offset in an axial direction of the cylindrical housing.
[0030] The symmetrical arrangement of the through holes realizes uniform fuel flow in the
cylindrical housing, stabilizing operation of the pressure-receiving plate when the
fuel pressure is increased. The axial offset arrangement of the through holes makes
it possible to adequately separate the opened or lightened portions in the axial direction,
thereby maintaining the strength of the housing at a sufficient value.
[0031] Another aspect of the present invention provides an accumulator fuel injection apparatus
for supplying accumulated fuel from an accumulator pipe to a fuel injector. The fuel
injector comprises a control chamber into which part of the accumulated fuel is introduced
to open-and-close control a needle valve according to a hydraulic pressure of the
introduced fuel, the needle valve determining injection and shutoff periods of the
fuel injector, an electromagnetic valve provided downstream of the control chamber
for opening and closing a fuel discharge passage of the control chamber to adjust
a hydraulic pressure in the control chamber, a switching leak passage for returning
the discharged fuel from a valve opening of the electromagnetic valve to a low-pressure
return passage, and a stationary leak passage for returning fuel leaking from slide
portions of the fuel injector to the low-pressure return passage. The electromagnetic
valve comprises an armature chamber for accommodating an armature driven by a solenoid
to open-and-close control the valve opening of the electromagnetic valve, and the
fuel is introduced into the armature chamber. The switching leak passage directly
connects the valve opening of the electromagnetic valve and the low-pressure return
passage. The armature chamber is provided in the stationary leak passage. A downstream
portion of the stationary leak passage, positioned downstream of the armature chamber,
communicates with an upper portion of the armature chamber. And, a damper element
is provided in the return passage at a portion downstream of the electromagnetic valve
for suppressing increase in a hydraulic pressure of fuel flowing in the return passage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The above and other objects, features and advantages of the present invention will
become more apparent from the following detailed description which is to be read in
conjunction with the attached drawings, in which:
Fig. 1 is vertical cross-sectional view showing an essential arrangement of a fuel
injector in accordance with a first embodiment of the present invention, employed
in an accumulator fuel injection apparatus;
Fig. 2 is a schematic view showing an overall arrangement of the accumulator fuel
injection apparatus embodying the present invention;
Fig. 3 is a vertical cross-sectional view showing an overall arrangement of the fuel
injector in accordance with the first embodiment of the present invention;
Fig. 4 is a perspective view showing an armature component involved in the fuel injector
used in the accumulator fuel injection apparatus in accordance with the first embodiment
of the present invention;
Fig. 5A is a graph showing operation of the accumulator fuel injection apparatus in
accordance with the first embodiment of the present invention;
Fig. 5B is a graph showing operation of a comparative conventional accumulator fuel
injection apparatus;
Fig. 6 is a vertical cross-sectional view showing an essential arrangement of a modified
fuel injector used in the accumulator fuel injection apparatus in accordance with
the first embodiment of the present invention;
Fig. 7 is a vertical cross-sectional view showing an essential arrangement of a fuel
injector in accordance with a second embodiment of the present invention, employed
in the accumulator fuel injection apparatus shown in Fig. 2;
Fig.8 is a vertical cross-sectional view showing an overall arrangement of a fuel
injector in accordance with a third embodiment of the present invention, employed
in the accumulator fuel injection apparatus shown in Fig. 2;
Fig. 9A is a front view showing a hollow screw used in the accumulator fuel injection
apparatus in accordance with the third embodiment of the present invention;
Fig. 9B is a cross-sectional view taken along a line I-I of Fig. 9A;
Fig. 10 is a time chart showing a valve lift behavior of the accumulator fuel injection
apparatus in accordance with the third embodiment of the present invention;
Fig. 11A is a front view showing a hollow screw used in the accumulator fuel injection
apparatus in accordance with a fourth embodiment of the present invention;
Fig. 11B is a cross-sectional view taken along a line II-II of Fig. 11A;
Fig. 12A is an enlarged across-sectional view showing a pressure-receiving plate accommodated
in the hollow screw shown in Fig. 11B;
Fig. 12B is a front view showing the pressure-receiving plate seen from an arrow X
of Fig. 12A;
Fig. 13 is a cross-sectional view showing operation of the hollow screw shown in Fig.
11B;
Fig. 14 is a time chart showing a valve lift behavior of a conventional accumulator
fuel injection apparatus; and
Fig. 15 is a vertical cross-sectional view showing an essential arrangement of a fuel
injector in accordance with a fifth embodiment of the present invention, employed
in the accumulator fuel injection apparatus shown in Fig. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Preferred embodiments of the present invention will be explained hereinafter with
reference to the attached drawings. Identical parts are denoted by the same reference
numerals throughout the views.
Overall Arrangement
[0034] Fig. 2 is a schematic view showing an overall arrangement of an accumulator fuel
injection apparatus embodying the present invention. A plurality of injectors 1, corresponding
to combustion chambers of respective cylinders of an engine (not shown), are provided.
A common rail 3 common to all cylinders is connected to these injectors 1 to supply
pressurized fuel. A supply pump 4 is connected to the common rail 3. Low-pressure
fuel is supplied to this supply pump 4 from a fuel tank 5 via a filter 6. The supply
pump 4 pressurizes the introduced fuel to a predetermined high level corresponding
to a fuel injection pressure, thereby accumulating the pressurized fuel in the common
rail 3.
[0035] The accumulated fuel supplied to the fuel injector 1 is chiefly injected into a corresponding
combustion chamber. However, part of the accumulated fuel is used to control opening
and closure of the fuel injector 1. The control fuel returns to the fuel tank 5 via
a return pipe 7 together with surplus fuel of the fuel injector 1 and the supply pump
4.
[0036] An electronic control unit (i.e., ECU) 8, associated with an electronic drive unit
(i.e., EDU) for driving the fuel injector 1, controls the fuel injector 1. The ECU
8 receives a signal of a pressure sensor 9 that detects the hydraulic pressure of
the common rail 3. The ECU 8 controls a fuel supply amount of the supply pump 4 so
as to equalize the hydraulic pressure of the common rail 3 to an optimum value which
is pre-determined in accordance with the engine load and the engine speed. Furthermore,
the ECU 8 receives signals obtained from various sensors, such as an engine speed
sensor and an engine load sensor, to judge the engine operating conditions. The ECU
8 determines an optimum injection timing and an optimum injection amount (i.e., injection
period of time) in accordance with the detected engine operating conditions, and generates
a control signal. In response to this control signal, the fuel injector 1 injects
the fuel into a corresponding chamber at the optimum timing with the optimum injection
amount.
First Embodiment
[0037] Fig. 1 is a vertical cross-sectional view showing an essential arrangement of the
fuel injector 1, employed in the accumulator fuel injection apparatus shown in Fig.
2. Fig. 3 is a vertical cross-sectional view showing an overall arrangement of the
fuel injector 1. The fuel injector 1 comprises a rodlike nozzle holder 108. A nozzle
body 101 is provided below the nozzle holder 108 via a distance piece 106 and fastened
by a nozzle retaining nut 107. The nozzle body 101 has a fuel injection hole 102 opened
at the distal end thereof. An electromagnetic valve 1a, determining fuel injection
and shutoff periods, is provided above the nozzle holder 108. The electromagnetic
valve 1a opens or closes its valve opening in response to a control signal supplied
from the ECU 8 (refer to Fig. 2).
[0038] The nozzle holder 108 has an inlet portion 109 and a return portion 110 each extending
obliquely upward. The inlet portion 109 is connected to the common rail 3 (refer to
Fig. 2). An inlet passage 201 is formed in the inlet portion 109. A bar filter 114
is provided in this inlet passage 201 at a portion downstream of an inlet opening
201a. The bar filter 114 removes foreign substances contained in the accumulated fuel
introduced from the common rail 3. A deep hole 113 is formed in the return portion
110. A hollow screw 115, screwed in the return portion 110, connects the return portion
110 and the return pipe 7 (refer to Fig. 2). A disc member 116 is placed at the bottom
of the deep hole 113. A portion communicating with the hollow screw 115 serves as
a return passage 213. A return passage 212 extends perpendicularly from the return
passage 213.
[0039] The nozzle body 101 has a vertical hole 103 extending along an axis "C" of the fuel
injector 1 and communicating with the fuel injection hole 102. A needle valve 105,
opening or closing the fuel injection hole 102, is provided in the vertical hole 103.
An upper half of the needle valve 105 is slidable with respect to the vertical hole
103.
[0040] A vertical hole 111, coaxial with the vertical hole 103, extends in the region corresponding
to the nozzle holder 108 and the distance piece 106. A circular hole 112, larger in
diameter than the vertical hole 111, is formed on an upper surface of the nozzle holder
108 at a portion corresponding to the open end of the vertical hole 111. The circular
hole 112 accommodates a lower plate 117 and an upper 118 each having a diameter smaller
than an inner diameter of the circular hole 112. The lower plate 117 closes the open
end of the vertical hole 111.
[0041] A solenoid cover 122 houses the plates 117 and 118 together with the valve parts
of the electromagnetic valve 1a, including a valve body 123. The solenoid cover 122
has a screwed portion engaged with a corresponding screwed portion of the nozzle holder
108. The circular hole 112, the plates 117 and 118, and the valve body 123 cooperatively
define a ring space 207 serving as a ring passage which communicates with the return
passage 212.
[0042] A piston 119, provided in the vertical hole 111, has a larger-diameter portion 119a
at an upper part thereof and a smaller-diameter portion 119b at a lower part thereof.
The larger-diameter portion 119a is slidably brought into contact with the vertical
hole 111. A spring 120 is provided around the smaller-diameter portion 119b. The needle
valve 105 is resiliently urged downward by the spring 120 via the piston 119. Thus,
the valve opening of the needle valve 105 is closed. The larger-diameter portion 119a
and the smaller-diameter portion 119b are separate parts which are connected after
the smaller-diameter portion 119b is inserted into the spring 120. The piston 119
thus assembled with the spring 120 is installed in the nozzle holder 108.
[0043] A control chamber 121 is provided above the piston 119. The upper end surface of
the piston 119, the vertical hole 111, and the lower end surface of the plate 117
define the wall of control chamber 121.
[0044] Next, the fuel passage of the fuel injector 1 will be explained. The inlet passage
201 bifurcates at a terminal end of the inlet portion 109 into two passages 202 and
203. The passage 202 extends downward and reaches the fuel injection hole 102 of the
nozzle body 101. Both the injection fuel and the open-and-close control fuel are supplied
through this passage 202. An injection chamber 104, formed at a predetermined position
of the passage 202, encircles a tapered recess 105a of the needle valve 105. When
the needle valve 105 receives the hydraulic pressure of the injection chamber 104,
the valve opening of the needle valve 105 is opened.
[0045] Next, the fuel passage for the fuel introduced from the inlet passage 201 and returned
to the return passage 213 will be explained. The passage 203, branching from the inlet
passage 201, extends upward and communicates with the control chamber 121 via a restrictor
204. The control chamber 121 communicates with the valve opening 124 of the electromagnetic
valve 1a via a fuel discharge passage 205 which extends upward across the plates 117
and 118 serving as the ceiling of the control chamber 121.
[0046] The valve opening 123 is defined by a valve seat 126 formed at an upper end of the
passage 205 and a ball 127 serving as a valve member disposed in a valve chamber 125.
The ball 127 is held by a shaft 128 that is slidable along the axis "C" in an up-and-down
direction.
[0047] A reversed V-shaped passage 206, formed in the valve body 123, has one end communicating
with the valve chamber 125. The other end of the reversed V-shaped passage 206 opens
at a ceiling surface of the ring passage 207. The reversed V-shaped passage 206 and
the ring passage 207 cooperatively form a switching leak passage 2a. When the valve
opening 124 is opened, the fuel flows through the switching leak passage 2a to the
return passages 212 and 213.
[0048] Both the hydraulic pressure of the control chamber 121 and the resilient force of
the spring 120 act on the needle valve 105 as a summed depression force for depressing
the needle valve 105 downward. The hydraulic pressure of the injection chamber 104
acts on the needle valve 105 as a lift force for lifting the needle valve 105 upward.
When the valve opening 124 is closed, the hydraulic pressure of the control chamber
121 is increased to a high level so that the depression force becomes larger than
the lifting force. The needle valve 105 moves downward. When the valve opening 124
is opened, the hydraulic pressure of the control chamber 121 is decreased to a low
level so that the depression force becomes smaller than the lifting force. The needle
valve 105 moves upward.
[0049] The up-and-down movement of the shaft 128 controls contact and separation between
the ball 127 and the valve seat 126 which cooperatively define the valve opening 124.
A push rod 131, extending along the axis "C", is provided above the shaft 128. A spring
130, housed in a spring chamber 129, resiliently urges the shaft 128 downward (i.e.,
in the valve closing direction) via the push rod 131.
[0050] A circular armature 133, housed in an armature chamber 132, is coaxially coupled
with the shaft 128. The armature 133 has a plurality of through holes 134 angularly
spaced at equal intervals, for reducing the resistance of fuel when the armature 133
moves in the up-and-down direction. A solenoid 135, comprising a circular core 136
with a coil 137 wound around this core 136, opposes the armature 133. When the solenoid
135 is activated in response to a signal fed from the ECU 8 (refer to Fig. 2), the
solenoid 135 magnetically attracts the armature 133. Thus, the shaft 128, coupled
with the armature 133, is lifted upward against the resilient force of the spring
130. Accordingly, activation of the solenoid 135 opens the valve opening 124 to decrease
the hydraulic pressure of the control chamber 121. The needle valve 105 lifts upward,
starting the injection of fuel. On the other hand, deactivation of the solenoid 135
closes the valve opening 124 to increase the hydraulic pressure of the control chamber
121. The needle valve 105 moves downward to stop the fuel injection.
[0051] The fuel leaking from the slide portions of the needle valve 105 and the piston 119
flows in the stationary leak passage 2b. A passage 208, extending in the up-and-down
direction across the nozzle holder 108 and the plates 117 and 118, serves as an upstream
portion of the stationary leak passage 2b. One end of the upstream portion 208 communicates
with a housing 111a of the spring 120 formed in the vertical hole 111 to return the
fuel leaking from the slide portions of the needle valve 105 and the piston 119. The
other end of the upstream portion 208 opens to a bottom surface of the armature chamber
132 via a bottom 113a of the deep hole 113 of the return portion 110.
[0052] A downstream portion 2b1 of the stationary leak passage 2b is a portion extending
from the armature chamber 132 to the ring passage 207. The ring passage 207 serves
as a merging portion to the switching leak passage 2a. More specifically, the armature
chamber 132 communicates via passage 209 with a ring passage 210 formed along an inner
periphery of the solenoid cover 122. The ring passage 210 communicates with the ring
passage 207 via a reversed L-shaped passage 211 formed in the valve body 123.
[0053] A ring passage 215, formed along the inner periphery of the solenoid cover 122, is
located above the ring passage 210 so as to communicate with this ring passage 210.
The ring passage 215 communicates with the spring chamber 129 via a passage 214. The
fuel leaks from the slide portion of the push rod 131 to the spring chamber 129 and
flows through the passage 214 and the ring passage 215 into the ring passage 210.
[0054] The armature chamber 132 has a cylindrical member 139 whose diameter is slightly
larger than that of the armature 133. The cylindrical member 139 is interposed between
the cylindrical holder 138 and the valve body 123. The cylindrical holder 138, coupled
around the solenoid 135 so as to hold the outer periphery of the solenoid 135, has
inner and outer diameters identical with those of the cylindrical member 139. The
lower end surface of the cylindrical holder 138 is flush with the lower end surface
of the solenoid 135. Accordingly, the lower end surface of the solenoid 135 is flush
with the upper end surface of the cylindrical member 139. The armature chamber 132
has a cylindrical wall defined by the cylindrical member 139, a ceiling defined by
the solenoid 135, and a bottom defined by the valve body 123.
[0055] Fig. 4 is a perspective view showing the cylindrical member 139. The cylindrical
member 139 has a total of four cutout portions 140 formed on a ring surface thereof
and spaced symmetrically at equal angularly intervals. When the cylindrical member
139 is installed between the valve body 123 and the cylindrical holder 138, the cutout
portions 140 face upward to form four passages 209 which open to an upper portion
corresponding to the ceiling 132a of the armature chamber 132.
[0056] Operation of the above-described fuel injection apparatus will be explained with
reference to Figs. 1 through 4. In the first operation of the fuel injection apparatus
performed after installation, the pressurized fuel is introduced into the inlet passage
201 from the common rail 3. The leaking fuel starts flowing in the stationary leak
passage 2b. The residual air contained in the armature chamber 132 moves to the upper
portion of the armature chamber 132. As the downstream portion 2b1 of the stationary
leak passage 2b opens to the ceiling 132a of the armature chamber 132, the collected
air is discharged out of the armature chamber 132 when the armature chamber 132 is
filled with the leaking fuel.
[0057] The leaking fuel flows into the armature chamber 132 via the upstream portion 208
of the stationary leak passage 2b, and moves upward. The fuel leaking from the slide
portions of the needle valve 105 or the like contains few bubbles. In the armature
chamber 132, few bubbles are generated. Accordingly, the bubbles quickly exit out
of the armature chamber 132 and come to the downstream portion 2b1 of the stationary
leak passage 2b which opens to the ceiling 132a of the armature chamber 132.
[0058] When the electromagnetic valve 1a is opened, the pressurized fuel of the control
chamber 121 flows into the valve chamber 125, generating a great amount of bubbles
in the vicinity of the valve opening 124. The generated bubbles flow into the return
passages 212 and 213 via the switching leak passage 2a without passing through the
armature chamber 132.
[0059] As described in the foregoing description, the armature chamber 132 is free from
the influence of the residual air contained during installation as well as the influence
of the bubbles generated in the vicinity of the valve opening 124. This realizes stabilized
operation of the armature.
[0060] Figs. 5A and 5B are graphs showing the fluctuation of the fuel injection amount with
respect to a set value in the accumulator fuel injection apparatus. Fig. 5A shows
test result obtained from the fuel injection apparatus in accordance with the present
invention, while Fig. 5B shows test result obtained from the conventional fuel injection
apparatus. In both cases, the common rail pressure was set to 128 MPa and the control
back pressure was set to 40 kPa. As apparent from the test data shown in Figs. 5A
and 5B, it was confirmed that the maximum fluctuation of the fuel injection amount
reaches approximately 0.7 mm
3/st according to the conventional apparatus but can be suppressed within approximately
0.4 mm
3/st in a wide range of the fuel injection amount according to the present invention.
This excellent performance is believed to be realized by the characteristic arrangement
of the present invention. Namely, the accumulator fuel injection apparatus of the
present invention prevents the bubbles generated in the vicinity of the valve opening
124 of the electromagnetic valve 1a from directly entering the armature chamber 132.
The air contained during installation and the bubbles contained in the leaking fuel
are smoothly discharged from the upper portion of the armature chamber 132 without
staying in the armature chamber 132. This stabilizes the operation of armature 133.
[0061] Although the above-described embodiment discloses four passages 209 between the ring
passage 210 and the armature chamber 132, the total number of the passages 209 can
be changed flexibly.
[0062] According to the above-described embodiment, the downstream portion of the stationary
leak passage opens to the wall of the armature chamber. However, it is possible to
form a passage in the core of the solenoid so that the downstream portion of the stationary
leak passage opens to the lower end of the core. It is desirable that the downstream
portion of the stationary leak passage opens closely to the ceiling of the armature
chamber as disclosed in the above-described embodiment. However, the opening position
may vary depending on the discharge behavior of bubbles or air in the armature chamber.
Therefore, it may be possible to set the opening position at a position slightly lower
than the ceiling when the bubbles or air can be smoothly discharged to the downstream
portion of the stationary leak passage.
[0063] Reducing the variation in the lift amount of the ball 127 is important to realize
accurate engine control. To this end, rotation of the armature 133 needs to be suppressed.
For example, as shown in Fig. 6, it is possible to provide a pin 141 protruding from
the bottom of the armature chamber 132. The pin 141 has a diameter slightly smaller
than that of the through holes 134 of the armature 133 so as to be engageable with
one of the through holes 134.
[0064] Both the ceiling 132a of the armature chamber 132 and the upper end surface of the
armature 133 are normal to the axis "C"in design, however their actual positions may
be slightly deviated from the designed positions due to insufficient accuracy in the
installation. This deviation causes the armature 133 to gradually rotate about the
axis "C" while the armature 133 repetitively reciprocates in the up-and-down direction.
Accordingly, when the armature 133 is dislocated with a predetermined angle, the periphery
of the armature 133 may hit the ceiling 132a of the armature chamber 132. As a result,
the lift amount of the ball 127 possibly varies. However, providing the pin 141 makes
it possible to prevent the armature 133 from rotating and, accordingly, the lift amount
of the ball 127 is stabilized.
Second Embodiment
[0065] Fig. 7 shows an essential arrangement of the second embodiment which can be added
to the above-described arrangement of the first embodiment shown in Figs. 1 through
4. The arrangement of the second embodiment is effective to reduce the influence of
the bubbles. Components identical with those shown in Figs. 1 through 4 are denoted
by the same reference numerals. In Fig. 7, the ring passage 207 has a check valve
142 provided at an open end of the ring passage 207. The check valve 142 comprises
a resiliently deflectable thin plate 143 made of a metal or a resin which is provided
on a ceiling surface 207a of the ring passage 207 for closing the opening of the passage
211. One side of the thin plate 143 is securely fixed to the ceiling surface 207a
by welding. An opening periphery 144 of the passage 211 serves as a valve seat of
the check valve 142. The thin plate 143 serves as a valve body.
[0066] The fuel flowing from the passage 211 to the ring passage 207 causes the thin plate
143 to resiliently deflect about the fixed side. The deflected portion of the thin
plate 143 separates from the ceiling surface 207a so as to open the valve opening
of the check valve 142. On the other hand, the fuel flowing from the ring passage
207 to the passage 211 causes the thin plate 143 to hermetically contact with the
ceiling surface 207a so as to close the valve opening of the check valve 142.
[0067] The bubbles may be generated in the vicinity of the valve opening 124 of the electromagnetic
valve 1a. However, providing the check valve 142 makes it possible to eliminate the
reverse flow of the bubbles directing from the ring passage 207 to the armature chamber
132. The ring passage 207 is the merging portion to the switching leak passage 2a.
The armature chamber 132 is located upstream of the passage 211. Thus, the second
embodiment makes the armature chamber 132 completely free from the influence of the
bubbles.
[0068] Although the above-described embodiment discloses the check valve 142 provided in
the ring passage 207, it is possible to provide the check valve 142 somewhere in the
downward portion 2b1 of the stationary leak passage 2b.
[0069] Needless to say, the check valve disclosed in the above-described embodiment can
be replaced by any other comparable valve.
Third Embodiment
[0070] Fig. 8 is a vertical cross-sectional view showing an overall arrangement of the fuel
injector 1 in accordance with a third embodiment of the present invention, employed
in the accumulator fuel injection apparatus shown in Fig. 2.
[0071] As shown in Fig. 8, the fuel injector 1 comprises a nozzle body 301 having a fuel
injection hole 302 opened at the distal end thereof, and a rodlike nozzle holder 303
holding the nozzle body 301. An electromagnetic valve 1a, determining fuel injection
and shutoff periods, is provided above the nozzle holder 303. The electromagnetic
valve 1a opens or closes its valve opening in response to a control signal supplied
from the ECU 8 (refer to Fig. 2).
[0072] The nozzle holder 303 has an inlet portion 304 and a return portion 305 each extending
obliquely upward. The inlet portion 304 is connected to the common rail 3 (refer to
Fig. 2). The return portion 305 is engaged with a hollow screw 502 at their screw
portions. The hollow screw 502 serves as a connection member for connecting the return
portion 305 and the return pipe 7 (refer to Fig. 2). A swivel fitting 7a, constituting
part of the return pipe 7, is connected to the return portion 305 together with the
hollow screw 502.
[0073] The hollow screw 502 is a characteristic portion of the present invention. Before
explaining details of the hollow screw 502, the fuel injector 1 will be explained
in more detail.
[0074] A needle valve 306, opening or closing the fuel injection hole 302, is slidably accommodated
in the nozzle bode 301. A piston 308, disposed above the needle valve 306, is slidable
in a guide hole 307 formed in the nozzle holder 303. The needle valve 306 is resiliently
urged downward by a spring 309 via the piston 308. Thus, the valve opening of the
needle valve 306 is closed. A control chamber 310 is formed above the piston 308.
An upper end surface 308a of the piston 308 constitutes a wall of the control chamber
310 shiftable in the up-and-down direction.
[0075] An inlet passage 311, formed in the inlet portion 304, has an inlet opening 311a
provided at the distal end of the inlet portion 304 for introducing the pressurized
fuel of the common rail 3. A bar filter 312 is provided in this inlet passage 311
at a portion downstream of the inlet opening 311a. The bar filter 312 removes foreign
substances contained in the accumulated fuel introduced from the common rail 3.
[0076] The inlet passage 311 bifurcates at a terminal end of the inlet portion 304 into
two passages 313 and 315. The passage 313 extends downward and reaches the fuel injection
hole 302 of the nozzle body 301. An injection chamber 314, formed at a predetermined
position of the passage 313, encircles a tapered recess 306a of the needle valve 306.
When the needle valve 306 receives the hydraulic pressure of the injection chamber
314, the valve opening of the needle valve 306 is opened.
[0077] The passage 315, branching from the inlet passage 311, extends upward and communicates
with the control chamber 310 via a restrictor 316. Both the hydraulic pressure of
the control chamber 310 and the resilient force of the spring 309 act on the needle
valve 306 as a summed depression force for depressing the needle valve 306 downward.
The hydraulic pressure of the injection chamber 314 acts on the needle valve 306 as
a lift force for lifting the needle valve 306 upward. When the hydraulic pressure
of the control chamber 310 is increased to a high level, the depression force becomes
larger than the lifting force. The needle valve 306 moves downward. When the hydraulic
pressure of the control chamber 310 is decreased to a low level, the depression force
becomes smaller than the lifting force. The needle valve 306 moves upward.
[0078] A passage 317 is formed above the control chamber 310. The control chamber 310 communicates
with a return passage 318 via this passage 317 and the electromagnetic valve 1a. The
return passage 318 is connected to a bottom of a hollow screw installation hole 319
formed in the return portion 305. Part of the accumulated fuel introduced from the
inlet portion 304 returns to the fuel tank 5 (refer to Fig. 2) of low-pressure via
a return passage R consisting of the passage 315, the restrictor 316, the control
chamber 310, the passage 317, the electromagnetic valve 1a, the return passage 318,
the hollow screw 502, and the return pipe 7.
[0079] The valve opening 320 of the electromagnetic valve 1a is defined by a valve seat
321 formed at an upper end of the passage 317 and a ball 322 serving as a valve member.
The return passage 318 communicates with a spring chamber 324 accommodating a spring
325 therein. The spring 325 resiliently urges the ball 322 downward (i.e., in the
valve closing direction) via the push rod 323. A circular armature 327, housed in
an armature chamber 326, is coaxially coupled with the upper end of push rod 323.
The armature chamber 326 communicates with the return passage 318.
[0080] A solenoid 329, provided above the armature 327, opposes the armature 327. When the
solenoid 329 is activated in response to a signal fed from the ECU 8 (refer to Fig.
2), the solenoid 329 magnetically attracts the armature 327. Thus, the push rod 323,
coupled with the armature 327, is lifted upward against the resilient force of the
spring 325. Accordingly, activation of the solenoid 329 opens the valve opening 320
to decrease the hydraulic pressure of the control chamber 310. The needle valve 306
lifts upward, starting injection of fuel. On the other hand, deactivation of the solenoid
329 closes the valve opening 320 to increase the hydraulic pressure of the control
chamber 310. The needle valve 306 moves downward to stop the fuel injection. The hollow
screw 502, as a characteristic part of the present invention, will be explained. Fig.
9A is an enlarged front view showing the hollow screw 502, and Fig. 9B is an enlarged
cross-sectional view of the hollow screw 502 taken along a line I-I of Fig. 9A. The
hollow screw 502 has a housing 401 opened at both ends. One open end of the housing
401 is closed by a cap 410 so as to define a chamber accommodating a damper element
502a.
[0081] The housing 401 is a cylindrical iron body configured into a bolt-like stepped tube
consisting of a larger-diameter head 402 and a smaller-diameter shaft 403. The iron
cap 410 is engaged with an opening of the head 402. An outer periphery of the head
402 is hexagonal. A screw portion 404 is formed on an outer surface of an opposite
end of the shaft 403. The hollow screw 502 is assembled with the swivel fitting 7a
and fixed to the return portion 305 (refer to Fig. 8) at the screw portion 404. The
inside space of the housing 401 serves as a return passage 405 communicating with
the return passage 318 of the fuel injector 1. A total of four through holes 406 are
provided on the cylindrical wall of the shaft 403. The swivel fitting 7a encircles
the shaft 403 so that the return passage 405 communicates with the return pipe 7.
[0082] Two pairs of through holes 406 are provided at symmetrical positions on the cylindrical
housing 401 corresponding to radial lines crossing normal to each other. The fuel,
returning from the fuel injector 1, uniformly flows in the return passage 405. These
two pairs of through holes 406 are offset in a direction of the axis "C"of the cylindrical
housing 401. With this axial offset arrangement of the through holes 406, the opened
or lightened portions are adequately separated in the axial direction. Thus, the strength
of the housing 401 is maintained at a sufficient value.
[0083] The cap 410 has a circular recess 411 facing the return passage 405. A ring ridge
412 is formed along a cylindrical periphery of the circular recess 411. A ring ridge
408, substantially identical with the ring ridge 412, is formed on an inside stepped
surface 407 of the housing 401 so as to oppose the ring ridge 412.
[0084] The damper element 502a, disposed between the housing 401 and the cap 410, comprises
two rubber O-rings 413 accommodated in a ring space defined by the ring ridges 408
and 412 and an inner cylindrical surface 409.
[0085] A circular plate 414, serving as a pressure-receiving plate, is sandwiched between
two rubber O-rings 413. The circular plate 414 is a thin stainless steel plate having
a thickness of approximately 0.1 mm. The diameter of the circular plate 414 is slightly
smaller than the inner diameter of the head 402 of the housing 401. The circular plate
414 hermetically contacts with the O-rings 413 at the peripheral edge thereof. The
circular plate 414 is disposed normal to the axis "C" of the housing 401 so as to
close the open end of the housing 401. The plate 414 is resiliently deflectable in
the direction of the axis "C" toward the cap 410 in response to an increased hydraulic
pressure of the fuel flowing in the return passage 405.
[0086] The O-ring 413 elastically deforms in accordance with an advancing depth of the cap
410 into the housing 401. To surely suppress the fuel leakage, it is preferable to
leave a margin in the elastic deformation of the O-ring 413 so that the O-ring 413
can elastically deform in response to the increased fuel pressure of the return passage
405. An overall deflection amount of the plate 414 is substantially increased by the
deformation of the O-ring 413. In other words, the plate 414 can be made of a relatively
strong or thick material.
[0087] In the assembling of the hollow screw 502, the plate 414 put between two O-rings
413 is placed in the recess of the head 402. Then, the cap 410 is press-fitted into
the opening of the head 402. Thereafter, the housing 401 and the cap 410 are completely
fixed by welding. A relatively low-temperature welding method, such as argon welding,
is preferable because the rubber O-ring 413 is not deteriorated.
[0088] Operation of the above-described accumulator fuel injection apparatus will be explained
with reference to Figs. 2, 8, 9A and 9B. To start the fuel injection, the ECU 8 activates
the solenoid 329. In response to the activation of the solenoid 329, the needle valve
306 lifts upward, starting the fuel injection.
[0089] When a predetermined fuel injection period of time has passed, the ECU 8 deactivates
the solenoid 329.
[0090] According to the conventional fuel injection apparatus, operation of the electromagnetic
valve is unstable during the valve closing operation, causing undesirable bounce of
the needle valve. However, according to the present invention, the hollow screw 502
has the damper element 502a comprising the plate 414 and the O-rings 413. When received
an increased hydraulic pressure of the fuel flowing in the return passage 405, the
plate 414 deflects toward the cap 410. The volume of the return passage 405 increases
in proportion to a deflection amount of the plate 414. Accordingly, the volume of
a portion of the return passage R, extending from the electromagnetic valve 1a to
the return passage 405, increases so as to cancel the increased fuel pressure. Thus,
the damper element 502b eliminates the fluctuation of the fuel pressure in the armature
chamber 326 of the electromagnetic valve 1a. The needle valve 306 surely closes its
valve opening in response to the termination of the fuel injection period of time,
holding the seated condition without causing any undesirable valve bouncing behavior.
[0091] According to the above-described embodiment, the damper element 502a is accommodated
in the hollow screw 502 which is located just downstream of the electromagnetic valve
1a. Thus, the damper element 502a can operate quickly in response to the change of
the fuel pressure. Furthermore, the plate 414 is normal to the axis "C" corresponding
to the flow direction of the fuel in the return passage 405. Thus, the plate 414 deflects
in the same direction as the fuel flow direction, effectively canceling the increase
of the fuel pressure.
[0092] Fig. 10 shows a valve lift behavior of the above-described accumulator fuel injection
apparatus, according to which the valve bouncing behavior responsive to the valve
closing operation is substantially eliminated. When compared with Fig. 14 that shows
the valve lift movement of the conventional accumulator fuel injection apparatus,
the difference is apparent. Thus, the present invention can provide an accumulator
fuel injection apparatus capable of performing accurate engine controls.
[0093] Furthermore, the hollow screw 502 of the present invention can be installed into
the fuel injector 1 in the same manner as a conventional one having no damper element.
The hollow screw 502 of the present invention is substantially the same in outer configuration
as that of the conventional one. No modification is required in the design of the
accumulator fuel injection apparatus. The above-described valve bouncing elimination
can be realized at low cost.
Fourth Embodiment
[0094] The hollow screw 502 disclosed in the third embodiment can be replaced by a hollow
screw 503 shown in Figs. 11A and 11B. Components identical with those disclosed in
Figs. 9A and 9B are denoted by the same reference numerals. Difference between the
third embodiment and the fourth embodiment will be chiefly explained hereinafter.
[0095] A housing 401A has a head 402A with a circular recess. A stepped portion 415 is formed
along an inner cylindrical wall of the head 402A, so that an inner diameter of the
circular recess slightly increases at the stepped portion 415. The cap 410A is inserted
into the radially enlarged portion of the circular recess. The cap 410A has a recess
416 having substantially the same inner diameter as that of a non-enlarged portion
of the circular recess formed in the head 402A.
[0096] A damper element of the second embodiment is constituted by a pressure-receiving
plate 414A only. A ring edge surface of the cap 410A opposes the surface of the stepped
portion 415 formed in the circular recess of the head 402A of the housing 401A. No
O-ring is used to hold the plate 414A between the ring edge surface of the cap 410A
and the stepped portion 415 of the housing 401A. The plate 414A serves as a wall of
the return passage 405.
[0097] Fig. 12A is an enlarged cross-sectional view showing the plate 414 of Fig. 11B. Fig.
12B is a front view of the plate 414 seen from an arrow X shown in Fig. 12A. The plate
414A is a circular thin stainless steel plate having a thickness of approximately
60 µm. Two, small and large, circular embossed ridges 417 and 418 are formed on the
surface of the circular plate 414A, coaxially about the center of the circular plate
414A. The plate 414A is elastically deformable at the embossed ridges 417 and 418.
When the plate 414A is installed between the cap 410A and the housing 401A, the plate
414A faces the return passage 405 at its recessed side opposed to the raised pattern
of the embossed ridges 417 and 418.
[0098] In the assembling of the hollow screw 503, the plate 414A is placed in the head 402A
of the housing 401A. Then, the cap 410A is press-fitted into the opening of the head
402A. Thereafter, the housing 401A and the cap 410A are hermetically fixed along their
cylindrical contact portions by brazing. The brazing is preferably used when no rubber
member is used.
[0099] According to the above-described arrangement, as shown in Fig. 13, the plate 414A
deflects at its embossed ridges 417 and 418 in response to the increased hydraulic
pressure of the fuel flowing in the return passage 405 during the valve closing operation.
The center of the plate 414A shifts toward the cap 410A. The volume of the return
passage 405 increases in proportion to a deflected amount of the plate 414A. Accordingly,
in the same manner as in the third embodiment, the valve bouncing behavior can be
surely prevented.
[0100] The position of the through holes formed on the hollow screw and the total number
thereof can be adequately changed unless operation of the damper element is worsened.
[0101] The above-described pressure-receiving plate deflects in response to the increased
fuel pressure so as to increase the substantial volume of the return passage. However,
in the arrangement of Fig. 9B, it is possible to use O-rings capable of causing a
large elastic deformation in response to the increased fuel pressure so that the pressure-receiving
plate moves backward in accordance with the elastic deformation of the O-rings. Alternatively,
it may be possible to remove the pressure-receiving plate when any other arrangement
for canceling the increased fuel pressure is adopted.
[0102] The installation position of the damper element is not limited in the hollow screw.
The damper element can be placed somewhere in the return passage downstream of the
electromagnetic valve, including the return pipe and the inside space of the fuel
injector. It is preferable to locate the damper element closely to the electromagnetic
valve. However, the installation position of the damper element can be adequately
determined according to an allowable level of the valve bouncing behavior.
Fifth Embodiment
[0103] Fig. 15 is a vertical cross-sectional view showing an essential arrangement of a
fuel injector 1 in accordance with a fifth embodiment of the present invention, employed
in the accumulator fuel injection apparatus shown in Fig. 2. The fuel injector 1 according
to the fifth embodiment is substantially the combination of essential structures of
the above-described first and third embodiments. More specifically, the hollow screw
115 of the first embodiment is replaced by the hollow screw 502 of the third embodiment.
The fifth embodiment can realize the effects of the above-described first and third
embodiments.
[0104] This invention may be embodied in several forms without departing from the spirit
of essential characteristics thereof. The present embodiments as described are therefore
intended to be only illustrative and not restrictive, since the scope of the invention
is defined by the appended claims rather than by the description preceding them. All
changes that fall within the metes and bounds of the claims, or equivalents of such
metes and bounds, are therefore intended to be embraced by the claims.
[0105] Pressurized fuel of a common rail (3) is introduced into a control chamber (121)
of a fuel injector (1). An electromagnetic valve (1a) opens or closes a fuel discharge
passage (205) of the control chamber (121) to adjust a hydraulic pressure of the control
chamber (121). Through a switching leak passage (2a), bubble-containing fuel directly
returns from a valve opening (124) of the electromagnetic valve (1a) to a low-pressure
return passage (212, 213) without passing through an armature chamber (132). Through
a stationary leak passage (2b), the fuel leaking from every slide portion returns
to the return passage (212, 213) via the armature chamber (132). A downstream portion
(2b1) of the stationary leak passage (2b) opens to the upper portion (132a) of the
armature chamber (132). A damper element (502a) is provided downstream of the electromagnetic
valve (1a) in the return passage for canceling an increased fuel pressure.
1. An accumulator fuel injection apparatus comprising:
a fuel injector (1);
an accumulator pipe (3) for supplying pressurized fuel to said fuel injector (1);
a control chamber (121; 310) for open-and-close controlling a needle valve (105; 306)
that determines injection and shutoff periods of said fuel injector (1); and
an electromagnetic valve (1a) for adjusting a hydraulic pressure of said control chamber
(121; 310);
characterized in that
stabilizing means is provided for stabilizing behavior of the fuel used to control
said fuel injector (1).
2. The accumulator fuel injection apparatus in accordance with claim 1, wherein said
electromagnetic valve (1a) comprising an armature (133) driven by a solenoid (135)
to open-and-close control a valve opening (124) of said electromagnetic valve (1a),
said armature (133) is accommodated in an armature chamber (132) into which the fuel
is introduced, and said stabilizing means is a passage (2b1) for discharging bubbles
or residual air from said armature chamber (132).
3. The accumulator fuel injection apparatus in accordance with claim 1, wherein said
stabilizing means is a damper element (502a) provided in a return passage (R) which
returning part of said pressurized fuel from said fuel injector (1) to a fuel tank
(5) via a return pipe (7), and said damper element (502a) is provided at a portion
downstream of said electromagnetic valve (1a) for suppressing increase in a hydraulic
pressure of fuel flowing in the return passage (R).
4. An accumulator fuel injection apparatus for supplying accumulated fuel from an accumulator
pipe (3) to a fuel injector (1),
said fuel injector (1) comprising:
a control chamber (121) into which part of the accumulated fuel is introduced to open-and-close
control a needle valve (105) according to a hydraulic pressure of the introduced fuel,
said needle valve (105) determining injection and shutoff periods of said fuel injector
(1), an electromagnetic valve (1a) for opening and closing a fuel discharge passage
(205) of said control chamber (121) to adjust a hydraulic pressure in said control
chamber, a switching leak passage (2a) for returning discharged fuel from a valve
opening (124) of said electromagnetic valve (1a) to a low-pressure return passage
(212, 213), and a stationary leak passage (2b) for returning fuel leaking from slide
portions of said fuel injector (1) to said low-pressure return passage (212, 213),
and
said electromagnetic valve (1a) comprising an armature chamber (132) for accommodating
an armature (133) driven by a solenoid (135) to open-and-close control the valve opening
(124) of said electromagnetic valve (1a), and the fuel is introduced into said armature
chamber (132),
characterized in that
said switching leak passage (2a) directly connects said valve opening (124) of said
electromagnetic valve (1a) and said low-pressure return passage (212, 213),
said armature chamber (132) is provided in said stationary leak passage (2b), and
a downstream portion (2b1) of said stationary leak passage (2b) positioned downstream
of said armature chamber (132) communicates with an upper portion (132a) of said armature
chamber (132).
5. The accumulator fuel injection apparatus in accordance with claim 4, wherein said
downstream portion (2b1) of said stationary leak passage (2b) is connected to an opening
provided at a height corresponding to a ceiling (132a) of said armature chamber (132).
6. The accumulator fuel injection apparatus in accordance with claim 4 or 5, wherein
said stationary leak passage (2b) has a check valve (142) provided between said armature
chamber (132) and a merging portion (207) to said switching leak passage (2a) for
limiting flow of said fuel in a single direction directing from said armature chamber
(132) to said merging portion.
7. An accumulator fuel injection apparatus comprising:
a fuel injector (1);
an accumulator pipe (3) for supplying pressurized fuel to said fuel injector (1);
a return passage (R) for returning part of said pressurized fuel from said fuel injector
(1) to a fuel tank (5) via a return pipe (7);
a control chamber (310) provided in said return passage (R) for open-and-close controlling
a needle valve (306) that determines injection and shutoff periods of said fuel injector
(1); and
an electromagnetic valve (1a) provided downstream of said control chamber (310) for
controlling communication and isolation between said control chamber (310) and said
return pipe (7),
characterized in that
a damper element (502a) is provided in said return passage (R) at a portion downstream
of said electromagnetic valve (1a) for suppressing increase in a hydraulic pressure
of fuel flowing in the return passage (R).
8. The accumulator fuel injection apparatus in accordance with claim 7, wherein said
damper element (502a) comprises a pressure-receiving plate (414, 414A) facing said
return passage (R, 405) and retractable in response to the increase of hydraulic pressure
of said fuel flowing in said return passage (R, 405).
9. The accumulator fuel injection apparatus in accordance with claim 7 or 8, wherein
said damper element (502a) is accommodated in a connection member (502, 503) connecting
said fuel injector (1) and said return pipe (7), and said connecting member constitutes
part of said return passage (R).
10. The accumulator fuel injection apparatus in accordance with claim 9, wherein said
connection member (502, 503) comprises a cylindrical housing (401, 401A) connected
to said fuel injector (1) at one end, said cylindrical housing (401, 401A) has at
least one through hole (406) formed on a cylindrical wall thereof for communicating
an inside space of said cylindrical housing (401, 401A) with said return pipe (7),
said damper element (502a) comprises a pressure-receiving plate (414, 414A) made of
a resiliently deflectable thin plate disposed normal to an axis (C) of said cylindrical
housing (401, 401A) to close the other end of said cylindrical housing (401, 401A).
11. The accumulator fuel injection apparatus in accordance with claim 10, wherein two
pairs of through holes (406) are provided at symmetrical positions on said cylindrical
housing (401, 401A) corresponding to radial lines crossing normal to each other, and
said two pairs of through holes (406) are offset in an axial direction of said cylindrical
housing (401, 401A).
12. An accumulator fuel injection apparatus for supplying accumulated fuel from an accumulator
pipe (3) to a fuel injector (1),
said fuel injector (1) comprising:
a control chamber (121) into which part of the accumulated fuel is introduced to open-and-close
control a needle valve according to a hydraulic pressure of the introduced fuel, said
needle valve determining injection and shutoff periods of said fuel injector (1),
an electromagnetic valve (1a) provided downstream of said control chamber (121) for
opening and closing a fuel discharge passage (205) of said control chamber (121) to
adjust a hydraulic pressure in said control chamber, a switching leak passage (2a)
for returning the discharged fuel from a valve opening (124) of said electromagnetic
valve (1a) to a low-pressure return passage (212, 213), and a stationary leak passage
(2b) for returning fuel leaking from slide portions of said fuel injector (1) to said
low-pressure return passage (212, 213), and
said electromagnetic valve (1a) comprising an armature chamber (132) for accommodating
an armature (133) driven by a solenoid (135) to open-and-close control the valve opening
(124) of said electromagnetic valve (1a), and the fuel is introduced into said armature
chamber (132),
characterized in that
said switching leak passage (2a) directly connects said valve opening (124) of said
electromagnetic valve (1a) and said low-pressure return passage (212, 213),
said armature chamber (132) is provided in said stationary leak passage (2b),
a downstream portion (2b1) of said stationary leak passage (2b) positioned downstream
of said armature chamber (132) communicates with an upper portion (132a) of said armature
chamber (132), and
a damper element (502a) is provided in said return passage at a portion downstream
of said electromagnetic valve (1a) for suppressing increase in a hydraulic pressure
of fuel flowing in the return passage.